Measurement of the double-beta decay half-life and search for the neutrinoless double-beta decay of Ca48 with the NEMO-3 detector

The NEMO-3 experiment at the Modane Underground Laboratory investigates the double-beta decay of Ca48. Using 5.25 yr of data recorded with a 6.99 g sample of Ca48, approximately 150 double-beta decay candidate events are selected with a signal-to-background ratio greater than 3. The half-life for the two-neutrino double-beta decay of Ca48 is measured to be T2ν1/2=[6.4+0.7−0.6(stat)+1.2−0.9(syst)]×1019  yr. A search for neutrinoless double-beta decay of Ca48 yields a null result, and a corresponding lower limit on the half-life is found to be T0ν1/2>2.0×1022  yr at 90% confidence level, translating into an upper limit on the effective Majorana neutrino mass of ⟨mββ⟩<6.0–26  eV, with the range reflecting different nuclear matrix element calculations. Limits are also set on models involving Majoron emission and right-handed currents.